This invention relates to arrangements for monitoring the operation of catalytic converters.
It is known to use catalytic converters for the conversion of harmful components in the exhaust gases of internal combustion engines, in particular, those used for operating motor vehicles. These catalysts include those which convert hydrocarbons and carbon monoxide contained in the exhaust gases into materials which are not injurious to health. The operating life of such catalysts is limited because they are exposed to great stresses in operation, in particular, high temperatures as well s jarring during the operation of the vehicle. This means that after a period of time, which depends on the mode of operation of the associated internal combustion engine, the conversion ratio of the catalyst is reduced to levels which require replacement of the catalytic converter.
For this reason, methods for monitoring of the conversion ratio of a catalytic converter are known, as described, for example, in German Patent No. 26 43 739. According to the patent, the temperature at various locations in the housing of a catalytic converter, such as upstream and downstream from the converter, is measured during operation of the converter. By a comparison of the measured temperature values, the conversion ratio is determined and a warning signal is generated in the event of a critical reduction in the conversion ratio. Aside from the fact that these known methods are only carried out at the end of the warm-up phase of the catalytic converter after its starting temperature has been reached, the known methods do not take into account the fact that the measured temperatures are dependent not only on the state of the catalytic converter, but especially on the load on the internal combustion engine at the time of measurement. Internal combustion engines for motor vehicles in particular have a large variation in load and in revolutions per minute so that the quantity of exhaust gases (and thus the flow velocity through the catalytic converter) and the exhaust gas temperature are subject to large variations. Therefore, such known methods, which are carried out in the course of normal operation of the internal combustion engine under varying load, do not provide an accurate indication of the specific degree of activity of the catalytic converter.